Interface structure

ABSTRACT

An interface structure for detachably interfacing a surgical robot arm to a surgical instrument, the interface structure comprising a main body; and a drive transfer element comprising a first portion and a second portion, the first portion being releasably engageable with a portion of the surgical robot arm and the second portion being releasably engageable with a portion of the surgical instrument; the drive transfer element being movable relative to the main body so as to enable transfer of drive between the surgical robot arm and the surgical instrument.

BACKGROUND

It is known to use robots for assisting and performing surgery. FIG. 1illustrates a typical surgical robot 100 which consists of a base 108,an arm 102, and an instrument 105. The base supports the robot, and isitself attached rigidly to, for example, the operating theatre floor,the operating theatre ceiling or a trolley. The arm extends between thebase and the instrument. The arm is articulated by means of multipleflexible joints 103 along its length, which are used to locate thesurgical instrument in a desired location relative to the patient. Thesurgical instrument is attached to the distal end 104 of the robot arm.The surgical instrument penetrates the body of the patient 101 at a port107 so as to access the surgical site. At its distal end, the instrumentcomprises an end effector 106 for engaging in a medical procedure.

FIG. 2 illustrates a typical surgical instrument 200 for performingrobotic laparoscopic surgery. The surgical instrument comprises a base201 by means of which the surgical instrument connects to the robot arm.A shaft 202 extends between the base 201 and an articulation 203. Thearticulation 203 terminates in an end effector 204. In FIG. 2, a pair ofserrated jaws are illustrated as the end effector 204. The articulation203 permits the end effector 204 to move relative to the shaft 202. Itis desirable for at least two degrees of freedom to be provided to themotion of the end effector 204 by means of the articulation.

A surgeon utilises many instruments during the course of a typicallaparoscopy operation. For this reason, it is desirable for theinstruments to be detachable from and attachable to the end of the robotarm with an ease and speed which enables instruments to be exchangedmid-operation. It is therefore desirable to minimise the time taken andmaximise the ease with which one instrument is detached from a robot armand a different instrument is attached.

The operating theatre is a sterile environment. The surgical roboticsystem must be sterile to the extent it is exposed to the patient.Surgical instruments are sterilised prior to use in an operation,however the robot arm is not sterilised prior to use. Instead, a steriledrape is placed over the whole of the surgical robot prior to theoperation. In this way, the patient is not exposed to the non-sterilesurgical robot arm. When exchanging instruments mid-operation, it isdesirable for the sterile barrier to be maintained.

SUMMARY

According to an aspect of the invention, there is provided an interfacestructure for detachably interfacing a surgical robot arm to a surgicalinstrument, the interface structure comprising:

-   -   a main body; and    -   a drive transfer element comprising a first portion and a second        portion, the first portion being releasably engageable with a        portion of the surgical robot arm and the second portion being        releasably engageable with a portion of the surgical instrument;    -   the drive transfer element being movable relative to the main        body so as to enable transfer of drive between the surgical        robot arm and the surgical instrument.

Suitably the drive transfer element is slidably movable relative to themain body.

Suitably the main body comprises a first side for facing the surgicalrobot arm and a second side for facing the surgical instrument, thefirst portion being disposed towards the first side and/or the secondportion being disposed towards the second side.

Suitably the main body comprises an aperture connecting the first sideand the second side, and the drive transfer element is configured so asto obstruct fluid flow through the aperture so as to maintain a sterilebarrier between the surgical robot arm and the surgical instrument.

Suitably the interface structure is configured so that the drivetransfer element obstructs fluid flow through the aperture as the drivetransfer element moves relative to the main body.

Suitably the interface structure is configured so that the drivetransfer element obstructs fluid flow through the aperture across theextent of movement of the drive transfer element relative to the mainbody.

Suitably the drive transfer element covers the aperture.

Suitably the main body defines a path along which the drive transferelement is movable.

Suitably the main body defines a linear path along which the drivetransfer element is movable.

Suitably the path defined by the main body comprises a slot within whichthe drive transfer element is receivable and along which the drivetransfer element is movable.

Suitably the path defined by the main body comprises a channel withinwhich the drive transfer element is receivable and along which the drivetransfer element is movable.

Suitably the channel is formed as a cavity or recess. The cavity orrecess may be within the main body.

Suitably the interface structure comprises a cover attachable to themain body, the channel being defined between a portion of the main bodyand a portion of the cover.

Suitably the cover is attachable to one of the first side and the secondside of the main body.

Suitably the drive transfer element comprises a central portion, thecentral portion comprising the first portion and the second portion, andan extending portion which extends away from the central portion.

Suitably the extending portion covers the aperture. Suitably the centralportion and the extending portion cover the aperture.

Suitably the extending portion is configured so that at an end of arange of motion of the drive transfer element relative to the main body,a distal end of the extending portion remains covered by the cover.

Suitably the drive transfer element is a rigid element.

Suitably the drive transfer element comprises a portion of movablematerial to which at least one of the first portion and second portionare attachable, the movable material being movable so as to accommodatemovement of the drive transfer element relative to the main body whilstpermitting the maintenance of the sterile barrier between the surgicalrobot arm and the surgical instrument.

Suitably the portion of movable material comprises a resilient material.

Suitably the interface structure comprises a roller, and the portion ofmovable material is windable onto the roller.

Suitably the interface structure comprises a plurality of drive transferelements.

Suitably the interface structure comprises a first drive transferelement which is movable relative to the main body along a first path.Suitably the first path is a linear path. Suitably the interfacestructure comprises a second drive transfer element which is movablerelative to the main body along a second path. Suitably the second pathis a linear path.

Suitably the interface structure comprises a first drive transferelement movable relative to the main body along a first linear path, anda second drive transfer element movable relative to the main body alonga second linear path, the first path and second path being parallel toone another.

Suitably the first path is parallel to a shaft of a surgical instrumentwhen the interface structure is interfaced with the surgical instrument.

Suitably at least one of the first path and the second path is alignedwith a shaft of a surgical instrument when the interface structure isinterfaced with the surgical instrument.

Suitably the interface structure comprises three drive transferelements, each drive transfer element being movable relative to the mainbody along a respective path, and each of the respective paths beingparallel to one another.

Suitably the main body of the interface structure comprises a deformablematerial. Suitably the main body of the interface structure comprises aresilient material.

The material of the main body disposed between the drive transferelements may comprise an unconstrained portion. The unconstrainedportion may permit movement of the drive transfer elements relative toone another.

Suitably the material of the main body disposed between the drivetransfer elements comprises a fabric material.

Suitably the main body of the interface structure comprises a rigidmaterial.

Suitably the paths of the first and second drive transfer elements arein the same plane. Suitably the path of the third drive transfer elementis in the same plane as the paths of the first and second drive transferelements.

The first path may be in a first plane. The second path may be in asecond plane. The first plane and the second plane may be different toone another. The third path may be in a third plane. The third plane maybe different to the first plane and/or the second plane. Suitably thethird plane is co-planar to the first plane or the second plane.Suitably at least two of the first plane, the second plane and the thirdplane are co-planar.

Suitably the first path is of a different length to the second path.Suitably the third path is the same length as at least one of the firstpath and the second path.

Suitably the main body comprises a first retention portion for retainingthe interface structure on at least one of the surgical robot arm andthe surgical instrument. Suitably the retention portion is arranged toengage with a second retention portion on the at least one of thesurgical robot arm and the surgical instrument.

Suitably the main body comprises a first retention portion for retainingthe interface structure on at least one of the surgical robot arm andthe surgical instrument, the retention portion being engageable with asecond retention portion on the at least one of the surgical robot armand the surgical instrument.

Suitably the interface structure is retainable on the surgical robot armto minimise relative movement between the main body of the interfacestructure and the surgical robot arm. Suitably the interface structureis retainable on the surgical instrument to minimise relative movementbetween the main body of the interface structure and the surgicalinstrument.

Suitably the first portion of the drive transfer element comprises oneof a recess and a protrusion.

Suitably the second portion of the drive transfer element comprises oneof a recess and a protrusion. Suitably where the first portion comprisesa recess, the second portion comprises a protrusion. Suitably where thefirst portion comprises a protrusion, the second portion comprises arecess.

Suitably the first portion of the drive transfer element comprises arecess for engagement with a protruding fin on the surgical robot armand the second portion of the drive transfer element comprises aprotrusion for engagement with a cup on the surgical instrument.Suitably the protrusion comprises a chamfer or rounded portion at itsdistal end. The chamfer or rounded portion may ease engagement of theprotrusion with the cup.

Suitably the protrusion comprises a cavity in communication with therecess. The recess may be continuous with the cavity in the protrusion,such that a fin receivable into the recess is permitted to extend intothe cavity. Suitably the protrusion of the second portion comprises acavity in communication with the recess of the first portion. The recessof the first portion may be continuous with the cavity in the protrusionof the second portion, such that a fin receivable into the recess ispermitted to extend into the cavity.

Suitably the main body comprises an alignment feature on at least one ofthe first side and the second side for aiding alignment of the interfacestructure with the surgical robot arm and/or the surgical instrumentduring engagement.

Suitably the alignment feature comprises a stud and/or aligning recess.The alignment feature may be engageable with a corresponding alignmentfeature on the surgical robot arm and/or on the surgical instrument.

Suitably a surgical drape extends from the interface structure.

Suitably the surgical drape extends from a periphery of the interfacestructure. Suitably the interface structure comprises a lip adjacent aperiphery of the interface structure, and the surgical drape extendsfrom the lip. The interface structure and the surgical drape may beintegrally formed.

According to an aspect of the invention, there is provided a roboticsurgical system comprising an interface structure as described above anda surgical robot arm, the surgical robot arm comprising a base and aplurality of articulations connecting the base to a drive assemblyinterface at or towards a distal end of the surgical robot arm, theplurality of articulations enabling the drive assembly interface to bearticulated relative to the base; the interface structure beingattachable to the drive assembly interface.

According to an aspect of the invention, there is provided a roboticsurgical system comprising an interface structure as described above anda surgical instrument for use in robotic surgery, the surgicalinstrument comprising a shaft, a surgical end effector at or towards adistal end of the shaft and an instrument interface at or towards aproximal end of the shaft; the interface structure being attachable tothe instrument interface.

Any one or more features of any aspect above may be combined with anyone or more features of that aspect and/or any other aspect above. Thesehave not been written out in full here for the sake of brevity.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will now be described by way of example withreference to the accompanying drawings. In the drawings:

FIG. 1 illustrates a surgical robot performing a surgical procedure;

FIG. 2 illustrates a known surgical instrument;

FIG. 3 illustrates a surgical robot;

FIG. 4 illustrates a drive assembly interface of a surgical robot arm;

FIG. 5 illustrates an instrument interface of a surgical instrument;

FIG. 6 illustrates the drive assembly interface of a robot arm withattached instrument;

FIG. 7a illustrates one side of an interface structure;

FIG. 7b illustrates the other side of the interface structure of FIG. 7a;

FIG. 8 illustrates an axial cross-sectional view of an instrumentinterfaced with a drive assembly via the interface structure of FIG. 7a;

FIG. 9 illustrates a side cross-sectional view of an instrumentinterfaced with a drive assembly via the interface structure of FIG. 7a;

FIG. 10a schematically illustrates a side view of an alternativeinterface structure;

FIG. 10b schematically illustrates a plan view of the alternativeinterface structure shown in FIG. 10a ; and

FIG. 11 schematically shows drive transfer elements of an alternativeinterface structure.

DETAILED DESCRIPTION

FIG. 3 illustrates a surgical robot having an arm 300 which extends froma base 301. The arm comprises a number of rigid limbs 302. The limbs arecoupled by revolute joints 303. The most proximal limb 302 a is coupledto the base by a proximal joint 303 a. It and the other limbs arecoupled in series by further ones of the joints 303. Suitably, a wrist304 is made up of four individual revolute joints. The wrist 304 couplesone limb (302 b) to the most distal limb (302 c) of the arm. The mostdistal limb 302 c carries an attachment 305 for a surgical instrument306. Each joint 303 of the arm has one or more motors 307 which can beoperated to cause rotational motion at the respective joint, and one ormore position and/or torque sensors 308 which provide informationregarding the current configuration and/or load at that joint. Suitably,the motors are arranged proximally of the joints whose motion theydrive, so as to improve weight distribution. For clarity, only some ofthe motors and sensors are shown in FIG. 3. The arm may be generally asdescribed in our co-pending patent application PCT/GB2014/053523.

The arm terminates in the attachment 305 for interfacing with theinstrument 306. Suitably, the instrument 306 takes the form describedwith respect to FIG. 2. The instrument has a diameter less than 8 mm.Suitably, the instrument has a 5 mm diameter. The instrument may have adiameter which is less than 5 mm. The instrument diameter may be thediameter of the shaft. The instrument diameter may be the diameter ofthe profile of the articulation. Suitably, the diameter of the profileof the articulation matches or is narrower than the diameter of theshaft. The attachment 305 comprises a drive assembly for drivingarticulation of the instrument. Movable interface elements of the driveassembly interface mechanically engage corresponding movable interfaceelements of the instrument interface in order to transfer drive from therobot arm to the instrument. One instrument is exchanged for anotherseveral times during a typical operation. Thus, the instrument isattachable to and detachable from the robot arm during the operation.Features of the drive assembly interface and the instrument interfaceaid their alignment when brought into engagement with each other, so asto reduce the accuracy with which they need to be aligned by the user.

The instrument 306 comprises an end effector for performing anoperation. The end effector may take any suitable form. For example, theend effector may be smooth jaws, serrated jaws, a gripper, a pair ofshears, a needle for suturing, a camera, a laser, a knife, a stapler, acauteriser, a suctioner. As described with respect to FIG. 2, theinstrument comprises an articulation between the instrument shaft andthe end effector. The articulation comprises several joints which permitthe end effector to move relative to the shaft of the instrument. Thejoints in the articulation are actuated by driving elements, such ascables. These driving elements are secured at the other end of theinstrument shaft to the interface elements of the instrument interface.Thus, the robot arm transfers drive to the end effector as follows:movement of a drive assembly interface element moves an instrumentinterface element which moves a driving element which moves a joint ofthe articulation which moves the end effector.

Controllers for the motors, torque sensors and encoders are distributedwithin the robot arm. The controllers are connected via a communicationbus to a control unit 309. The control unit 309 comprises a processor310 and a memory 311. The memory 311 stores in a non-transient waysoftware that is executable by the processor to control the operation ofthe motors 307 to cause the arm 300 to operate in the manner describedherein. In particular, the software can control the processor 310 tocause the motors (for example via distributed controllers) to drive independence on inputs from the sensors 308 and from a surgeon commandinterface 312. The control unit 309 is coupled to the motors 307 fordriving them in accordance with outputs generated by execution of thesoftware. The control unit 309 is coupled to the sensors 308 forreceiving sensed input from the sensors, and to the command interface312 for receiving input from it. The respective couplings may, forexample, each be electrical or optical cables, or may be provided by awireless connection. The command interface 312 comprises one or moreinput devices whereby a user can request motion of the end effector in adesired way. The input devices could, for example, be manually operablemechanical input devices such as control handles or joysticks, orcontactless input devices such as optical gesture sensors. The softwarestored in the memory 311 is configured to respond to those inputs andcause the joints of the arm and instrument to move accordingly, incompliance with a pre-determined control strategy. The control strategymay include safety features which moderate the motion of the arm andinstrument in response to command inputs. Thus, in summary, a surgeon atthe command interface 312 can control the instrument 306 to move in sucha way as to perform a desired surgical procedure. The control unit 309and/or the command interface 312 may be remote from the arm 300.

FIGS. 4 and 5 illustrate an exemplary mechanical interconnection of thedrive assembly interface and the instrument interface in order totransfer drive from the robot arm to the instrument. FIG. 4 illustratesan exemplary drive assembly interface 400 at the end of a robot arm 404.The drive assembly interface 400 comprises a plurality of drive assemblyinterface elements 401, 402, 403. The drive assembly interface elementsprotrude from surfaces 406, 407, 408 on the drive assembly interface400. The protrusion of the drive assembly interface elements from thedrive assembly interface 400 permits engagement of the drive assemblyinterface elements with corresponding instrument interface elements, asdescribed below. The protrusions are in the form of fins in theillustrated example. In other implementations, other types of protrusioncan be provided. The drive assembly interface elements suitably comprisea stiff material, such as a metal. Suitably the protrusion is formedfrom a stiff material, such as a metal. Preferably the drive assemblyinterface element is formed from a stiff material, such as a metal.

The protrusions (the fins in the illustrated example) comprise a chamfer414 at their distal ends. The chamfer provides for ease of engagement ofthe protrusions in corresponding recesses, as described below. In otherexamples the distal ends of the protrusions can be provided with arounded corner. The edges of the chamfered portions can be rounded.

The fins extend through the surfaces 406, 407, 408. The portions of thefins that protrude from the surfaces are perpendicular to the plane ofthe surfaces. In other examples the fins can protrude in a directionthat is within a range of 10 degrees from perpendicular. Preferably thedirection in which the fins extend is within a range of 5 degrees orwithin a range of 2 degrees from perpendicular.

FIG. 4 illustrates three drive assembly interface elements. In otherexamples, there may be greater than or fewer than three drive assemblyinterface elements. The drive assembly interface elements 401, 402, 403are movable within the drive assembly interface 400 along linear paths409, 410, 411. The paths can be parallel with one another. Suitably atleast two of the paths are parallel. The paths need not be preciselyparallel with one another. There may be some tolerance in how closelyaligned the paths need to be. For example, the paths may be within 10degrees of each other. The paths may extend in respective directionswithin a 10 degree range. Preferably the paths are within 5 degrees ofeach other, or within 2 degrees or 1 degree of each other. The paths mayextend in respective directions within a 5 degree range, or preferably a2 degree or 1 degree range.

Aligning the paths in this manner can assist in providing correspondingmechanisms more compactly. For instance, the mechanisms can be arrangedto move alongside one another, permitting the mechanisms to be arrangedmore closely together.

In the illustrated example, the linear paths 409, 410, 411 are disposedon two parallel planes. The central linear path 410 is disposed on aplane 407 set into the drive assembly interface 400 compared to that inwhich the outer two linear paths 409, 411 are disposed. This arrangementpermits a more compact interface between the drive assembly interface400 and an instrument interface 500, as will be described below.

In other implementations, the three linear paths 409, 410, 411 can bedisposed on the same plane, or all on different planes. In anotherexample, the outer two linear paths 409, 411 are disposed on a plane setinto the drive assembly interface 400 compared to that in which thecentral linear path 410 is disposed. In implementations utilisingdiffering numbers of drive assembly interface elements, differentconfigurations of planes on which the paths are disposed are possible.

The drive assembly interface 400 comprises a recessed portion 412 forreceiving a portion of the instrument. This arrangement can permit amore compact configuration when the instrument is mounted onto the robotarm.

Referring now to FIG. 5, the shaft 501 of the instrument terminates inthe instrument interface 500. The instrument interface 500 comprises aplurality of instrument interface elements (one of which is shown at 502in FIG. 5; these can more clearly be seen in FIG. 6 at 502, 507, 509).The instrument interface elements suitably comprise a stiff material,such as a metal. Suitably the instrument interface element is formedfrom a stiff material, such as a metal. Pairs of driving elements (onesuch pair is shown at 503, 504) extend into the instrument interface 500from the end of the shaft 501. Each pair of driving elements terminatesin one of the instrument interface elements. In the example shown inFIG. 5, the driving element pair 503, 504 terminates in instrumentinterface element 502; likewise, other driving element pairs terminatein corresponding instrument interface elements.

In the illustrated example there are three driving element pairs thatterminate in three instrument interface elements. In other examples,there may be greater than or fewer than three instrument interfaceelements. There may be greater than or fewer than three driving elementpairs. In FIG. 5 there is a one-to-one relationship between instrumentinterface elements and driving element pairs. In other examples, theremay be any other coupling relationship between the instrument interfaceelements and driving element pairs. For example, a single instrumentinterface element may drive more than one pair of driving elements. Inanother example, more than one instrument interface element may drive asingle pair of driving elements.

Each instrument interface element 502, 507, 509 comprises a recess, orcup 505, which is the portion of the instrument interface elementengageable with the drive assembly interface element.

The instrument interface elements are displaceable within the instrumentinterface. In the example shown, the instrument interface elements areslideable along rails. Instrument interface element 502 is slideablealong rail 506. Instrument interface element 507 is slideable along rail508. Instrument interface element 509 is slideable along rail 510. Eachinstrument interface element is displaceable along a direction parallelto the direction of elongation of the pair of driving elements whichthat instrument interface element holds captive. Each instrumentinterface element is displaceable in a direction parallel to thelongitudinal axis 512 of the instrument shaft 501. When the instrumentinterface element moves along its respective rail, it causes acorresponding movement to the driving element pair secured to it. Thus,moving an instrument interface element drives motion of a drivingelement pair and hence motion of a joint of the instrument.

Drive assembly interface 400 mates with instrument interface 500. Theinstrument interface 500 comprises structure for receiving the driveassembly interface elements 401, 402, 403. Specifically, the instrumentinterface elements 507, 502, 509 receive drive assembly interfaceelements 401, 402, 403. In the example shown, each instrument interfaceelement comprises a socket or cup 505 for receiving the fin of thecorresponding drive assembly interface element. The socket 505 of oneinstrument interface element 502 receives a fin of the correspondingdrive assembly interface element 402. Similarly, sockets of the otherinstrument interface elements receive fins of the other drive assemblyinterface elements.

Each drive assembly interface element is displaceable within the driveassembly. This displacement is driven. For example, the displacement maybe driven by a motor and lead screw arrangement. In the example shown,the drive assembly interface elements are slideable along drive rails802, 804. Each drive assembly interface element is coupled to one driverail. Referring to FIG. 8, the right-hand drive assembly interfaceelement 403 is coupled to a right-hand drive rail 804. The central driveassembly interface element 402 is coupled to a left-hand drive rail 802.Whilst not shown, the left-hand drive assembly interface element 401 iscoupled to the left-hand drive rail 802. In other configurations, thecentral drive assembly interface element is coupled instead to theright-hand drive rail 804, or to both of the left-hand drive rail 802and the right-hand drive rail 804.

Coupling the central drive assembly interface element 402 to both theleft-hand drive rail and to the right-hand drive rail assists instabilising the central drive assembly interface element. For thearrangement illustrated in FIG. 8, where the central drive assemblyinterface element is elongate in the vertical direction of FIG. 8, thiscan reduce bending or rotation of the central drive assembly interfaceelement as it moves and drives the corresponding drive transfer element.

Each drive assembly interface element is displaceable along a directionparallel to the longitudinal axis 413 of the terminal link of the robotarm. When the drive assembly interface element moves along its rail, itcauses a corresponding movement to the instrument interface element towhich it is engaged. Thus, driving motion of a drive assembly interfaceelement drives motion of an instrument interface element which drivesarticulation of the end effector of the instrument.

The portions of the fins that protrude from the surfaces comprise frontand rear faces aligned in the directions of movement of the driveassembly interface elements. Here, front and rear refer to movement inone direction, when the front face will face the direction of movementand the rear face will face away from the direction of movement. Whenthe drive assembly interface element moves in the opposite direction,the front face will face away from the direction of movement and therear face will face the direction of movement.

The front and rear faces of the drive assembly interface elements aretransverse to the direction in which the drive assembly interfaceelements are driveably movable. The front and rear faces of the driveassembly interface elements are parallel to the direction in which thefins protrude from the surfaces. The front and rear faces need not beexactly parallel to this direction, but are preferably within a range of10 degrees, or within a range of 5 degrees, or more preferably within arange of 2 degrees of this direction.

The socket 505 comprises an interior face that is transverse to thedirection in which the instrument interface elements are movable. Theinterior face need not be exactly transverse to this direction, but ispreferably within a range of 10 degrees, or within a range of 5 degrees,or more preferably within a range of 2 degrees of being transverse tothis direction.

In the illustrated example the interior face of the instrument interfaceelements and the front and rear faces of the drive assembly interfaceelements are parallel to one another. This can assist in the transferralof drive between the elements.

In FIGS. 4 and 5 there is a one-to-one relationship between instrumentinterface elements and drive assembly interface elements. In otherexamples, there may be any other coupling relationship between theinstrument interface elements and drive assembly interface elements. Forexample, a single drive assembly interface element may drive more thanone instrument interface element. In another example, more than onedrive assembly interface element may drive a single instrument interfaceelement.

FIG. 6 illustrates the instrument being placed into engagement with therobot arm. When drive assembly interface element 401 is held captive byinstrument interface element 507, drive assembly interface element 402is held captive by instrument interface element 502, and drive assemblyinterface element 403 is held captive by instrument interface element509, the instrument interface elements and the drive assembly interfaceelements are all displaceable in the same direction. This direction isparallel to both the longitudinal axis 413 of the terminal link of therobot arm 404 and the longitudinal axis 512 of the instrument shaft 501.

During an operation or surgical procedure, the surgical robot isshrouded in a sterile drape to provide a sterile barrier between thenon-sterile surgical robot and the sterile operating environment. Thesurgical instrument is sterilised before being attached to the surgicalrobot. The sterile drape is typically constructed of a plastic sheet,for example made of polyester, polypropylene, polyethylene orpolytetrafluoroethylene (PTFE). Suitably, the drape is flexible and/ordeformable.

The sterile drape does not pass directly between the drive assemblyinterface 400 and the instrument interface 500. The drape comprises aninterface structure 700 for interfacing between the drive assemblyinterface 400 and the instrument interface 500. FIGS. 7a and 7b show anexemplary interface structure 700 in isolation. The interface structure700 is also shown in FIG. 6 attached to the drive assembly interface 400and to the instrument interface 500. The interface structure 700 may beintegrally formed with the drape. Alternatively, the interface structure700 may be formed separately from the drape and subsequently attached tothe drape. Either way, the interface structure 700 is sterile. One side701 of the interface structure 700 directly contacts the drive assemblyinterface. The other side 702 of the interface structure 700 directlycontacts the instrument interface. Thus, the interface structure 700prevents the non-sterile drive assembly interface from directly touchingthe sterile instrument interface and hence maintains the sterile barrierbetween the two components.

The interface structure 700 comprises a main body 704 and drive transferelements 706, 707, 708. The drive transfer elements are movable relativeto the main body. Conveniently, when the interface structure 700 isattached to the surgical robot arm, the main body 704 lies parallel tothe surface(s) of the drive assembly interface 400. Suitably in thisattached configuration, the main body 704 is aligned with the driveassembly interface.

The main body 704 comprises a first side 701 which faces the robot armwhen the instrument is attached to the robot arm. Specifically, thefirst side 701 faces the drive assembly 400. The main body 704 comprisesa second side 702 opposite to the first side. The second side 702 facesthe instrument when the instrument is attached to the robot arm.Specifically, the second side 702 faces the instrument interface 500.Suitably both the first side 701 and the second side 702 aresubstantially flat. The first side and the second side need not becompletely flat. Being substantially flat, or flat over at least aportion of its surface (for example over at least 10% of its surface,over at least 20% of its surface, over at least 30% of its surface,preferably over at least 40% of its surface or more preferably over atleast 50% of its surface) permits the interface structure 700 to becompactly sandwiched between the instrument and the robot arm when theinstrument is attached to the robot arm.

Being flat can include having flat portions in different planes. Forexample, as illustrated in FIG. 4, the drive assembly interface 400 canhave portions which are flat, but disposed generally over two planes, asdescribed above. Suitably the interface structure 700 is configured tocorrespond to the general surface features of the drive assemblyinterface so as to compactly engage therewith, reducing or minimisinggaps or space between the interface structure and the drive assemblyinterface.

The main body 704 comprises an aperture. In the interface structure 700illustrated in FIGS. 7a, 7b and 8, an aperture is located generallycentral to the main body 704, though it need not be located in thisposition. In the illustrated example, the main body 704 comprises threeapertures: a first aperture 816, a second aperture 817 and a thirdaperture 818 (as can be seen in FIG. 8). The apertures 816, 817, 818provide for communication between the first side 701 and the second side702 though the main body 704.

A cover 710 is provided which covers a portion of the main body 704. Thecover covers the part of the main body that comprises the apertures. Inthe illustrated implementation, the cover 710 is located on the secondside 702 of the main body 704. In other examples, the cover can belocated on the first side 701 of the main body, or covers can be locatedon both sides of the main body. The cover 710 is attached to the mainbody 704. Suitably the cover 710 is fixed to the main body 704. Thecover can be attached to the main body by adhesive, or by any otherconvenient means or method of attachment.

The cover 710 comprises further apertures, or slots. In the illustratedexample, the cover 710 comprises a first slot 726, a second slot 727 anda third slot 728. The slots communicate with the apertures in the mainbody 704. The first slot 726 is aligned with the first aperture 816; thesecond slot 727 is aligned with the second aperture 817; the third slot728 is aligned with the third aperture 818. Thus the slots in the cover710 provide fluid flow paths between the first side and the second side702 of the main body.

The apertures 816, 817, 818 in the main body 704 define paths alongwhich the drive transfer elements are movable. In the exampleillustrated in FIGS. 7a and 7b , the paths are linear paths. The firstaperture 816 defines a first path; the second aperture 817 defines asecond path; the third aperture 818 defines a third path.

The main body 704 and the cover 710 define therebetween channels alongwhich drive transfer elements are movable. Suitably the drive transferelements are slideable within the channels. Referring to FIG. 8, a lip819 adjacent an aperture in the main body 704 and a corresponding lip820 adjacent an aperture in the cover 710 define a channel 821 betweenthe lips. The main body 704 and the cover 710 define two channels peraperture, one to either side of the aperture. The channels extend alongthe length of the apertures.

As mentioned above, the interface structure 700 comprises drive transferelements. In the example illustrated in FIGS. 7a and 7b , the interfacestructure comprises three drive transfer elements: a first drivetransfer element 706, a second drive transfer element 707 and a thirddrive transfer element 708. The first drive transfer element 706 isslidably received in the first slot 726. The second drive transferelement 707 is slidably received in the second slot 727. The third drivetransfer element 708 is slidably received in the third slot 728. Eachdrive transfer element is slidably movable along its respective slot.

The drive transfer elements comprise a central portion and an extendingportion which extends away from the central portion. With reference tothe first drive transfer element 706, the central portion 736 comprisesa protrusion. The extending portion 716 comprises a flat plate thatextends from the central portion 736. The extending portion 716 iselongate in two opposite directions which, when the first drive transferelement 706 is located in the first slot 726, are aligned with thedirections in which the first slot 726 extends. In directions transverseto these directions, i.e. in directions transverse to the extent of theslots, the first drive transfer element comprises a first lip 846 as canbe seen from FIG. 8. The first lip 846 is receivable into channels toeither side of the first aperture 816. Similarly, a second lip 847 onthe second drive transfer element 707 is receivable into channels toeither side of the second aperture 817. A third lip 848 is receivableinto channels to either side of the third aperture 818. Suitably thedrive transfer elements are rigid.

The drive transfer elements extending along the slots restricts thefluid flow path through the apertures. The drive transfer elementsextending into the channels adjacent the apertures restricts the fluidflow path through the apertures. In this way the drive transfer elementsrestrict the fluid flow path around the drive transfer elements.

Suitably the inter-engagement between the drive transfer elements 706,707, 708 and the main body 704 is such as to restrict the fluid flowpath between the drive transfer elements and the main body. Thisinter-engagement is, for example, by a portion of the drive transferelements being retained adjacent the main body, such as by beingretained in the slots, or by being retained in the channels.

The first slot 726 comprises a first end 730 and a second end 731opposite the first end, along the length of the first slot. Theextending portion 716 of the first drive transfer element 706 comprisesa first extension 732 and a second extension 734. The length of thefirst extension 732 from the central portion 736 of the first drivetransfer element 706 is L1. The length of the second extension 734 fromthe central portion 736 of the first drive transfer element 706 is L2.

At the furthest extent of movement of the first drive transfer element706 towards the second end 731 of the first slot 726, the distancebetween the central portion 736 and the first end 730 is D1. At thefurthest extent of movement of the first drive transfer element 706towards the first end 730 of the first slot 726, the distance betweenthe central portion 736 and the second end 731 is D2.

The length of the first extension L1 is at least the same as thedistance D1. Suitably L1 is greater than D1, for example to provide anoverlap between the first extension and the main body and/or between thefirst extension and the cover. The length of the second extension L2 isat least the same as the distance D2. Suitably L2 is greater than D2,for example to provide an overlap between the first extension and themain body and/or between the first extension and the cover. In this way,the extending portion 716 (comprising the first extension 732 and thesecond extension 734) covers the aperture. In other words, it covers thespace between the central portion and the ends of the slots. Providingthe extension portions 732, 734 to be the same length as, or greaterthan, the potential gap means that the gap will remain coveredthroughout the extent of movement of the drive transfer element withinthe slot.

The second drive transfer element 707 and the third drive transferelement 708 are similarly configured. For example, the second drivetransfer element 707 comprises a third extension 735. Thus each apertureor slot remains covered throughout the whole extent of movement of therespective drive transfer element.

Referring to FIGS. 7a and 7b , the slots are not all of equal length.The second slot 727 is shorter than the first slot 726 and the thirdslot 728. The slots need not be sized in this particular way. Each slotcan be sized as desired to account for or permit the required movementof the respective drive transfer element. In this example the centraldrive assembly interface element 402 is configured to move along ashorter linear path 410 than the linear paths 409, 411 along which theleft-hand drive assembly interface element 401 and the right-hand driveassembly interface element 403 are configured to move. Correspondinglythe first slot 726 and the third slot 728 are longer than the secondslot 727. In the illustrated example the first drive transfer elementand the third drive transfer element have a relative movement withrespect to the main body of ±5.1 mm (i.e. 10.2 mm from one end to theother). The second drive transfer element has a relative movement withrespect to the main body of ±3 mm (i.e. 6 mm from one end to the other).The relative movements need not be the same as these. In some examplesthe relative movement of the first and third drive transfer elements islonger or shorter than this. The relative movement of the second drivetransfer element can be longer or shorter than this. The ratio ofrelative movements need not be this ratio, but could be greater or lessthan this ratio.

As can be seen from FIG. 9, the ends 910 of the slot in the cover arefurther apart than the ends 911 of the aperture in the main body. Theslot in the cover is longer than the respective aperture in the mainbody. This additional length permits the socket 502 to protrude at leastpartially within the slot in the cover without reducing the travel ofthe drive transfer element within the aperture. Suitably the additionallength of the slot compared to the aperture is at least equal to thewidth of that portion of the socket disposed between the drive transferelement and the end 910 of the slot. Suitably the additional length ofthe slot compared to the aperture is at least equal to twice the widthof that portion of the socket disposed between the drive transferelement and the end 910 of the slot, so as to avoid reducing the travelof the drive transfer element within the aperture at either end of therange of movement.

The protrusion of the socket 502 at least partially within the slot inthe cover permits better coupling between the socket and the drivetransfer element. The protrusion of the socket at least partially withinthe slot in the cover permits better coupling between the socket and thefin. The coupling is improved by providing a greater overlap between thesocket and the fin in the direction of drive transfer.

In the illustrated example the slots are aligned at one end. An end ofthe first slot proximal to an indent 712 in the interface structure 700is aligned with an end of the second slot proximal to the indent 712 andan end of the third slot proximal to the indent 712. When the drivetransfer elements are moved, for example by being driven, to theirfurthest extent towards the indent 712, each of the drive transferelements will be aligned with the others. Where the ends of the slots,or the drive transfer elements, are aligned, they may be at the samedistance as one another along a length of the interface structure.

In other examples, the length of the slots need not match the length ofthe linear paths. Suitably the slots are at least as long as the linearpaths.

This arrangement assists in restricting fluid flow through the apertureor slot. Restricting this fluid flow assists in maintaining a sterilebarrier. Thus when attached to a surgical robot arm, and/or to asurgical instrument, the interface structure can assist in maintainingthe sterile barrier between the arm and the instrument.

As mentioned above, the central portion 736 of the first drive transferelement 706 comprises a protrusion to the second side 702 of theinterface structure 700. As can be seen from FIG. 7a , each of the drivetransfer elements comprises a central portion which comprises aprotrusion to the second side 702 of the interface structure 700. Inthis example, the central portions of the drive transfer elementscomprise recesses to the first side 701 of the interface structure 700(visible in FIG. 7b ) for engagement with the fins of the respectivedrive assembly interface elements.

In other examples, the central portions of the drive transfer elementscan be arranged the other way round. In other words, recesses can beprovided towards the second side and protrusions can be provided towardsthe first side. Alternatively, any combination of protrusions andrecesses can be provided. This can include one drive transfer elementcomprising either both a protrusion towards the first side and aprotrusion towards the second side, or a recess towards the first sideand a recess towards the second side. The configuration adopted willsuitably match that of the drive assembly interface 400 and theinstrument interface 500. In other words, where a drive assemblyinterface element comprises a protruding fin, the central portion of therespective drive transfer element towards the first side will comprise arecess for receiving the fin. Where the drive assembly interface elementcomprises a recess, the central portion of the respective drive transferelement towards the first side will comprise a protrusion for engagingwith the recess. Similarly, where the instrument interface elementcomprises a protruding fin, the central portion of the respective drivetransfer element towards the second side will comprise a recess forreceiving the fin. Where the instrument interface element comprises arecess, the central portion of the respective drive transfer elementtowards the second side will comprise a protrusion for engaging with therecess.

Suitably the drive transfer elements comprise a plastic material.Preferably the drive transfer elements are able to deform slightly so asto accommodate interfacing with the drive assembly interface elementsand/or the instrument interface elements. Preferably the drive transferelements engage with the drive assembly interface elements by aninterference fit, such as a light interference fit. Suitably the drivetransfer elements engage with the instrument interface elements by aninterference fit, such as a light interference fit.

Generally, each drive transfer element comprises a first portion and asecond portion. The central portion suitably comprises the first portionand the second portion. The first portion is engageable with the robotarm. For example, the first portion is engageable with the driveassembly interface, such as being engageable with a drive assemblyinterface element. The second portion is engageable with the instrument.For example, the second portion is engageable with the instrumentinterface, such as being engageable with an instrument interfaceelement.

To put it another way, at least one of the first portion and the secondportion can be a drive transfer element recess, or a recess in the drivetransfer element. At least one of the first portion and the secondportion can be a drive transfer element protrusion, or a protrudingportion of the drive transfer element. Preferably, the drive transferelement comprises both a drive transfer element recess and a drivetransfer element protrusion.

The drive transfer element recess is engageable with an interfaceprotrusion, such as a protrusion on a drive assembly interface elementor on an instrument interface element. The drive transfer elementprotrusion is engageable with an interface recess, such as a recess in adrive assembly interface element or in an instrument interface element.

Referring to the illustrated example, the first portion comprises arecess and the second portion comprises a protrusion. The protrusion ofthe second portion comprises a chamfer and/or rounded edge to easeengagement of the protrusion with a cup, such as a cup on an instrumentinterface element, into which the protrusion is receivable. In theillustrated example, as best seen from FIGS. 7a and 9 the protrusion ofthe second portion has a V-shape in cross-section. This aids in engagingthe protrusion with the cup. The V-shape of the protrusion canaccommodate misalignment between the protrusion and the cup as theinstrument is attached to the interface structure. The recess of thefirst portion comprises a flared and/or rounded edge adjacent theopening into the recess to ease engagement with a protrusion or fin,such as a protrusion or fin on a drive assembly interface element, withwhich the recess is engageable.

Preferably, the first portion and the drive assembly interface elementcomprise cooperating surfaces which are complementary to one another.Preferably, the second portion and the instrument interface elementcomprise cooperating surfaces which are complementary to one another.Referring to FIG. 9, an interior of the cup of the instrument interfaceelement is shaped to be complementary to an exterior of the protrusionon the drive transfer element, and an interior of the drive transferelement is shaped to be complementary to an exterior of the protrusionof the drive assembly interface element.

Where one of the first portion and the second portion is a recess andthe other of the first portion and the second portion is a protrusion,the recess 901 can communicate with a cavity 902 in the protrusion 903,as can be seen from FIG. 9. A fin 930 receivable into the recess can bereceivable into the cavity through the recess. This can provide a morestable engagement between the drive assembly and the interfacestructure, between the interface structure and the instrument, and/orbetween the drive assembly and the instrument.

The drive transfer element comprises an outer edge or wall 904. Theouter wall 904 faces to the left in FIG. 9. The outer wall 904 faces adirection in which the drive transfer element can be driven by the driveassembly interface element. The outer wall 904 contacts, or engageswith, a socket inner wall 905 of the socket or cup 502 of the instrumentinterface element. The socket inner wall 905 faces an opposingdirection, such as an opposite direction, to that faced by the outerwall 904. In the illustrated example, the outer wall 904 and the socketinner wall 905 face in opposite directions. The drive transfer elementcomprises an inner edge or wall 906. The inner wall 906 faces to theright in FIG. 9. The inner wall 906 opposes a direction in which thedrive transfer element can be driven by the drive assembly interfaceelement. For example, referring to FIG. 9, the inner wall 906 isopposite to a direction in which the drive transfer element can bedriven (the drive transfer element can be driven to the left, and theinner wall 906 faces to the right). The inner wall 906 contacts, orengages with, a portion of the drive assembly interface element. In theillustrated example the drive assembly interface element comprises aprotrusion or fin 930 which contacts the inner wall 906 of the drivetransfer element. Thus drive is transferable from the drive assemblyinterface element 930 to the inner wall 906 of the drive transferelement, and from the outer wall 904 of the drive transfer element tothe socket inner wall 905.

The outer wall 904 and the socket inner wall 905 overlap one another inthe direction in which the drive transfer element is movable, i.e. inthe direction in which drive is transferrable between the drive assemblyinterface element and the instrument interface element. Suitably theouter wall 904 overlaps the whole of the socket inner wall 905.

Increasing, or maximising, the overlap between the outer wall 904 andthe socket inner wall 905, in other words increasing the area ofoverlap, can reduce, or minimise, the pressure on the drive transferelement. Thus a greater overlap reduces pressure between the driveassembly interface element and the instrument interface element.Pressure could be reduced by increasing the width of the overlap. Thismight, however, cause the width of the interfaces to increase, all otherthings remaining equal. Preferably, where the width of overlap isincreased, this is accommodated within the interfaces to avoid needingto increase the overall width of the interfaces.

Pressure could be reduced by increasing the height, or vertical (withrespect to FIG. 9) extent, of the overlap. This might, however, causethe height of the interfaces to increase, all other things remainingequal. Preferably, where the height of overlap is increased, this isaccommodated within the interfaces to avoid needing to increase theoverall height of the interfaces. One way of achieving this is toprovide the drive assembly interface element and instrument interfaceelement at relative positions such that the vertical overlap isincreased without affecting the overall height of the structure.Providing the cup 502 (which in the example illustrated in FIG. 9 islocated on the instrument interface element, but which, as describedabove, could alternatively be located on the drive assembly interfaceelement) so as to at least partially protrude within the slot, asdescribed above, can lead to an increase in the area of overlap withoutnecessarily causing the overall height to increase.

In a similar manner, another outer wall (for example a second outerwall) of the drive transfer element faces to the right (in FIG. 9). Thesecond outer wall faces another direction in which the drive transferelement can be driven by the drive assembly interface element. Thesecond outer wall contacts, or engages with, another socket inner wall(for example a second socket inner wall) of the socket 502. The secondsocket inner wall faces an opposing direction, such as an oppositedirection, to that faced by the second outer wall. The drive transferelement comprises a second inner edge or wall. The second inner wallopposes the other direction in which the drive transfer element can bedriven by the drive assembly interface element. The second inner wallcontacts, or engages with, a portion of the drive assembly interfaceelement. Thus drive is transferable from the drive assembly interfaceelement to the second inner wall of the drive transfer element, and fromthe second outer wall of the drive transfer element to the second socketinner wall.

The second outer wall and the second socket inner wall overlap oneanother in the direction (to the right in FIG. 9) in which the drivetransfer element is movable, i.e. in the direction in which drive istransferrable between the drive assembly interface element and theinstrument interface element. Suitably the second outer wall overlapsthe whole of the second socket inner wall.

The outer wall and the socket inner wall are, in the example illustratedin FIG. 9, parallel to one another. The second outer wall and the secondsocket inner wall are, in the example illustrated in FIG. 9, parallel toone another. In other examples, either or both pairs of walls need notbe parallel to one another.

The inner wall and a wall of the drive assembly interface elementarranged to be adjacent the inner wall are, in the example illustratedin FIG. 9, parallel to one another. The second inner wall and a wall ofthe drive assembly interface element arranged to be adjacent the secondinner wall are, in the example illustrated in FIG. 9, parallel to oneanother. In other examples, either or both of these pairs of walls neednot be parallel to one another.

The overlap of the outer wall and the socket inner wall (and/or of thesecond outer wall and the second socket inner wall) permits drive to betransferred by a compressive force, such as a substantially compressiveforce. Where the pairs of walls are parallel to one another, and thewalls are transverse to the direction in which drive is transferable,the force will be a compressive force. An increasing deviation from thisarrangement will result in a reduction in the compressive component ofthe force, and an increase in other components of the force, for examplebending or shear components.

In other examples, drive need not be transferred via overlappingportions of the walls. Drive can be transferable, at least in part, viaa portion of the drive transfer element which does not overlap with thedrive assembly interface element in the direction of drive transfer. Forexample, drive can be transferable via the V-shaped portion of the drivetransfer element (or, more generally, via a rounded and/or chamferedportion of the drive transfer element). This arrangement may provide agreater positional tolerance between the drive transfer element and theinstrument interface element whilst still being able to transfer drive.An interference fit, though preferable also in this arrangement, wouldagain not be necessary. In such an arrangement, a force which isvertical in the orientation of FIG. 9 is likely to be advantageouslyprovided to assist in keeping the drive assembly interface elements andthe instrument interface elements in an engaged configuration as driveis transferred.

The size or width of an opening (in a direction in which drive istransferrable) of the drive transfer element recess 901 is larger thanthat of the cavity 902. Referring to FIG. 9, both the recess and thecavity are provided centrally in the drive transfer element in aleft-right direction, i.e. one in which the drive transfer element ismovable. Since the recess has a larger width than the cavity, the innerwalls of the recess are not co-planar with the inner walls of thecavity. The inner walls of the recess are outwardly offset from theinner walls of the cavity.

This offsetting of the internal walls of the drive transfer elementrecess and the cavity can permit the interface protrusion to be engagedwithin the cavity without being engaged by the walls of the drivetransfer element recess. This arrangement can assist in providing drivetransfer through the walls of the cavity. In turn, this can assist inreducing the bending moment on the drive transfer element when beingdriven. This arrangement can reduce the components of the drive transferforce other than the compressive component.

Suitably the drive transfer element protrusion comprises a chamfer orrounded portion at or towards its distal end to ease engagement of thedrive transfer element protrusion with the interface recess. Suitablythe drive transfer element recess comprises a chamfer or rounded portionat its opening to ease engagement of the interface protrusion with thedrive transfer element recess. Referring to FIG. 9, the offsetting ofthe walls of the recess from the walls of the cavity provide a lipbetween the recess and the cavity. Suitably the lip is angled or roundedto ease engagement of the interface protrusion with the cavity throughthe drive transfer element recess and past the lip.

The drive assembly interface element comprises an elongate protrudingportion and a drive assembly interface element body 920. The elongateprotruding portion is receivable into the drive transfer element recess901. A strengthening and/or stiffening portion 921 is provided on thedrive assembly interface element proximal to the drive assemblyinterface element body 920. Referring to FIG. 9, the strengthening orstiffening portion is a buttress portion. In other examples thestrengthening or stiffening portion is a strut, or other abutment orfillet, or a gusset. The strengthening or stiffening portion can be anycombination of these. The strengthening or stiffening portion can bemade of a stronger and/or stiffer material than the drive assemblyinterface element body, for example titanium. Preferably thestrengthening or stiffening portion 921 is provided on the sides of thedrive assembly interface element towards and/or away from a direction inwhich the drive assembly interface element is movable. The strengtheningor stiffening portion, such as the buttress portion, suitably resistsbending of the drive assembly interface element, for example as thedrive assembly interface element is moved or driven. Suitably the driveassembly interface element is strong enough and/or stiff enough towithstand a force of at least 80N without breaking. Suitably the driveassembly interface element is strong enough and/or stiff enough towithstand a force of at least 130N without breaking. Suitably the driveassembly interface element can resist a force of at least 80N, andpreferably of at least 130N.

The interface structure comprises a first fastener 740 for retaining theinterface structure 700 on the robot arm when the interface structure ismounted, or attached, to the robot arm. The drive assembly interface 400comprises a retention lip 440. The first fastener 740 is engageable withthe retention lip 440. The first fastener 740 comprises a ridge 742.During attachment of the interface structure 700 to the drive assembly400, the ridge 742 passes over the retention lip 440. The first fasteneris resilient to permit flexing so that the ridge 742 can pass over theretention lip 440. Once the first fastener has passed the retention lip,a flat portion 743 at the rear of the first fastener (in the directionof attachment) abuts a front portion of the retention lip (again, in thedirection of attachment) and resists movement of the interface structure700 in a direction away from the robot arm along the longitudinal axis413 of the distal end 404 of the arm. In this way, the interfacestructure 700 is retained in position attached to the drive assemblyinterface 400. To remove the interface structure 700 from the robot arm,the first fastener can be released. The first fastener 740 is releasableby resiliently deforming the first fastener so as to lift the ridge 742over the retention lip 440. In the example illustrated in FIGS. 7a and7b , the first fastener comprises a tab 744. The tab 744 permits a userto lift the first fastener so as to disengage the ridge 742 from theretention lip 440. The tab 744 need not be provided in all examples. Theengagement of the first fastener with the retention lip can providetactile feedback that the interface structure is correctly or properlyattached to the robot arm.

Additional retention features are provided on an edge 750 of theinterface structure 700 in the illustrated example. As illustrated inFIG. 7b , one edge 750 of the interface structure comprises on aninternal face thereof two lugs 751, 752. The lugs 751, 752 protrudeinwardly from the internal face of the edge 750 of the interfacestructure 700. Cooperating retention features are provided on an outeredge of the drive assembly interface 400. Two passages 451, 452 areprovided on the outer edge of the drive assembly interface 400 whichcommunicate with a retention channel 453. In the illustrated example acommon retention channel communicates with both passages, but this neednot be the case. In alternatives, each passage can communicate with arespective retention channel. The passages 451, 452 and the retentionchannel 453 are formed as recesses in the outer edge of the driveassembly interface 400.

As the interface structure 700 is mounted to the drive assemblyinterface 400, the lugs 751, 752 will pass through the passages 451, 452and into the retention channel 453. The interface structure 700 can bemoved along the longitudinal axis 413 of the distal end of the arm 404.The retention channel 453 is parallel to the longitudinal axis 413 ofthe distal end of the arm. The movement of the interface structure inthis direction (i.e. parallel to the longitudinal axis 413) moves thelugs along the retention channel 453 away from the openings to thepassages 451, 452. At the same time, the first fastener 740 is moved toengage with the retention lip 440. When the lugs 751, 752 are moved awayfrom the openings to the passages 451, 452, the interface structure willbe restricted to move along the longitudinal axis 413 of the arm 404.The lugs 751, 752 will abut an upper edge 454 of the retention channel453 to restrict movement of the interface structure 700 away from thedrive assembly interface 400 in a direction transverse to thelongitudinal axis 413. In other words, the engagement of the lugs in theretention channel will prevent or restrict the interface structure frombeing lifted off the drive assembly.

As can be seen from FIG. 7b , in this example the lugs 751, 752 comprisean upright portion 753, 754. As the interface structure is moved alongthe longitudinal axis 413 of the distal end of the arm 404 so as toengage the lugs in the retention channel 453, the front face of theupright portions 753, 754 will move into abutment with faces 455, 456adjacent the passages 451, 452. This abutment between the uprightportions 753, 754 and the faces 455, 456 serves to limit the movement ofthe interface structure, and provides tactile feedback that the limit oftravel has been reached. The upright portions 753, 754 need not beprovided in every example.

This combination of retention features of the interface structure 700,i.e. the first fastener 740 and the lugs 751, 752, restrict the removalof the interface structure 700 from the robot arm. The interfacestructure is suitably configured to fully engage with the drive assemblyinterface whilst being moved a distance along the longitudinal axis 413of the arm that is the same as or less than the distance of travel of adrive transfer element permitted by the shortest slot (i.e. in theexample above, a distance of up to 6 mm). The drive transfer elements ofthe interface structure engage with the drive assembly interfaceelements as the interface structure is mounted on the drive assembly. Asthe main body of the interface structure is moved relative to the driveassembly so as to engage the retention features of the interfacestructure with those of the drive assembly, the drive transfer elementsare restricted in movement by virtue of being engaged with the driveassembly elements. Thus as the interface structure is moved intoengagement, the drive transfer elements will move relative to the mainbody. Restricting the possible extent of travel of the main bodyrelative to the drive assembly interface to the same as or less than theextent of travel of the drive transfer element with the shortest travelcan prevent that drive transfer element from being urged past its extentof travel. This can reduce potential damage to the interface structure,and assist in maintaining the sterile barrier.

In one example, prior to attaching the interface structure to the driveassembly interface, the drive assembly interface elements are driven toa desired position, such as an interfacing position. Suitably theinterfacing position, or the desired position, is for engaging the driveassembly interface elements with respective instrument interfaceelements. This desired position is suitably with the drive assemblyinterface elements at one end of their respective travel, for instancetowards the end of the drive assembly interface away from the proximalend of the robot arm. The interface structure can be arranged so thatthe drive transfer elements are correspondingly at cooperating positionswithin their respective travel, for instance with one of the drivetransfer elements (suitably the drive transfer element with the shortestextent of travel) being at one end of its respective travel. In thisway, the engagement of the drive transfer elements with the driveassembly interface elements is reliably effected. This method ofengagement can be done without needing to drive or otherwise move thedrive transfer elements and/or the drive assembly interface elementsback and forth to effect engagement.

Engaging the interface structure with the drive assembly in this way canmean that the main body of the interface structure is then able to moverelative to the drive assembly interface by up to the full travel of thedrive transfer element with the shortest travel.

To determine whether the drive assembly interface elements are in, orhave been driven to, the desired position, in one example the driveassembly comprises a sensor. Preferably the drive assembly comprises aplurality of sensors, a respective one for each drive assembly interfaceelement. The sensor is configured to sense the position of therespective drive assembly interface element. The sensor senses, ordetermines, when that drive assembly interface element passes athreshold position, such as a pre-determined or known position along theextent of travel of that drive assembly interface element. Suitably thesensor comprises at least one of a magnetic sensor, such as a Hallsensor, a light sensor, a capacitive sensor, an inductive sensor, anacoustic sensor, and a microswitch. Any suitable position-determiningsensor can be used. The sensor can be a proximity sensor. The sensor canbe a position sensor associated with the drive assembly interfaceelement.

The sensor, in the example schematically illustrated in FIG. 9,comprises two parts. A first part 912 of the sensor is provided in abody of the drive assembly. A second part 913 of the sensor is providedon the drive assembly interface element. As the drive assembly interfaceelement is moved, the first part 912 moves relative to the second part913. The first part 912 and the second part 913 are configured tointeract with one another. In one example the first part 912 comprises amagnetic sensor and the second part 913 comprises a magnet. The magneticsensor is configured to sense the magnet. The magnetic sensor isconfigured to output a first signal when the magnet is proximal to themagnetic sensor and a second signal when the magnet is distal from themagnetic sensor. Suitably the magnetic sensor is configured, orcalibrated, so that the output changes from the second signal to thefirst signal when the magnet, and hence the drive assembly interfaceelement, is less than a predetermined distance from the magnetic sensor.Thus when the magnetic sensor outputs the first signal, it can bedetermined that the drive assembly interface element is adjacent themagnetic sensor. The first part 912 of the sensor is located in thedrive assembly so that the drive assembly interface element is adjacentthe first part 912 of the sensor when it is in the desired position.

The drive assembly comprises a communication unit 914 for communicatingwith the control unit 309. The communication unit can be a wired and/ora wireless unit, and/or can couple the sensor, for example the firstpart 912 of the sensor, to the control unit 309 via a communication bus.Instead of or as well as the sensor determining the position of thedrive assembly interface element and/or determining whether it is in itsinterfacing position, the processor is configured to receive signals,such as the first signal and the second signal, from the sensor and independence on the received signals to determine the position of thedrive assembly interface element and/or to determine whether it is inits interfacing position. The processor can make such determinations independence on one or more of an algorithm and a reference table (such asa look-up table), which may be in a local memory 311 or remote memory.

Suitably where the sensor comprises a passive and an active part, thesecond part 913 comprises the passive part, such as the magnet, and thefirst part 912 comprises the active part, such as the magnetic sensor.The first part 912 can more easily be connected, for example by wires,to a power source and/or to the communication unit 914.

In some examples there is some play or tolerance in the location orposition of the drive transfer elements. The play or tolerance may beprovided by a small flexibility or deformation in the material of thedrive transfer elements. There might be some play or tolerance in thelocation of the drive transfer elements in a direction along the lengthof the main body, and/or transverse to this direction. There may be someplay or tolerance in the location of the drive transfer elementsperpendicular to the main body. This play or tolerance is suitably smallcompared to the extent of movement of the drive transfer elements, forexample to maintain positional determinability of the drive transferelements. The play or tolerance can be less than 1 mm, for example lessthan 0.5 mm or preferably less than 0.25 mm.

The play or tolerance can, in one example, be provided by the distancebetween the channels to either side of an aperture in the main body ofthe interface structure being slightly greater than the width of theextending portion that is arranged to slide within the channels. Theplay or tolerance can, in one example, be provided by the height of achannel to one side of an aperture in the main body of the interfacestructure being slightly greater than a height or thickness or theextending portion that is arrange to slide within the channel. As anexample, where the distance between the channels and/or the height ofthe channel or channels exceeds the respective width and/or thickness ofthe extending portion by 0.2 mm, there is a play or tolerance of 0.2 mmprovided. Other values for this play or tolerance are possible.

As described above, there are provided two lugs on one side of theinterface structure. Similarly, two lugs can be provided on the otherside of the interface structure, as illustrated in FIG. 7b .Correspondingly the outer edge of the other side of the drive assemblyinterface can be provided with passages and a retention channel forreceiving the lugs. In other examples a differing number of lugs can beprovided on each inner side of the interface structure 700. The numbersof lugs on each side need not be the same. Preferably there is at leastone lug on each side of the interface structure, though in some examplesa lug need only be provided on one side of the interface structure.Providing lugs on both sides can assist in retaining the interfacestructure on the arm. Such a retention can be more stable and/oreffective where at least one lug is provided on each side of theinterface structure.

Suitably the number of passages on the outer edges of the drive assemblyinterface 400 correspond to the number of lugs on the inner edges of theinterface structure, though this need not be the case. The number ofpassages on the outer edges of the drive assembly interface 400 issuitably at least the same as the number of lugs on the correspondingside of the interface structure.

As mentioned above, the retention channel can be common to all passages.In other examples a retention channel can communicate with fewer thanthe total number of passages on the respective side of the driveassembly interface. Each retention channel can communicate with one ormore passage.

In some examples, the passages and/or the retention channels cancomprise raised portions over which the lugs pass as the interfacestructure is attached to the robot arm. The raised portions may comprisedetents. Such raised portions can provide tactile feedback that theinterface structure is properly or correctly attached. The raisedportions can provide additional resistance to inadvertent removal of theinterface structure from the robot arm.

With the arrangement described above, the interface structure 700 isarranged to be mounted to the drive assembly interface 400 by placing itonto the drive assembly interface and then sliding it towards the robotarm (i.e. generally towards the right in the orientation of FIG. 4).

The interface structure 700 comprises a front face 760. The interfacestructure comprises an indent 712 towards the front face. The front faceis shaped to accommodate the indent. Similarly, the drive assemblyinterface 400 comprises a corresponding indent 412. The drive assemblyinterface comprises a front face 460. As the interface structure isattached to the drive assembly interface, the indent 712 of theinterface structure will at least partially pass into the indent 412 ofthe drive assembly interface. As the interface structure is slid alongthe longitudinal axis 413 of the distal end of the arm, the inner sideof the front face 760 of the interface structure will abut the frontface 460 of the drive assembly interface. This can restrict theinterface structure from being slid too far, and can help ensure that itis correctly or properly mounted to the drive assembly interface. Theindent 712 in the interface structure can act, for example together withthe indent 412 of the drive assembly, as an alignment feature to assistin the alignment of the interface structure and the drive assembly.

The indent 712 in the interface structure 700 can permit a more compactarrangement. The indent is shaped and configured, or sized, to receivethe shaft 501 of the instrument when the instrument is attached to theinterface structure. More particularly, the indent is shaped andconfigured, or sized, to receive a shaft attachment 610 located at theproximal end of the shaft 501 to the instrument interface 500. Theprovision of the indent 712, and the corresponding indent 412 in thedrive assembly interface 400 permits the instrument to be mounted to therobot arm with the longitudinal axis 512 of the instrument shaft 501closer to the longitudinal axis 413 of the distal end of the robot arm404. Preferably the instrument is mountable to the robot arm so that thelongitudinal axis 512 of the instrument shaft 501 is collinear with thelongitudinal axis 413 of the distal end of the robot arm 404.

Another feature which can permit a more compact arrangement is thearrangement of the drive transfer elements on different planes.Referring again to FIG. 7a , the second drive transfer element 707 ismovable along a plane lower (in the perspective of the figure) than thatin which the first and third drive transfer elements 706, 708 aremovable. This offsetting of the drive transfer elements of the interfacestructure 700 permits a corresponding offsetting of the drive assemblyinterface elements and the instrument interface elements. Thus the driveassembly interface 400 and the instrument interface 500 can beconfigured to be more compact in a direction lateral to the direction inwhich the drive interface elements are movable when the interfacestructure is attached to the robot arm and the instrument. In otherwords, locating the central drive transfer element off-plane withrespect to the outer drive transfer elements (in either direction) canpermit the outer drive transfer elements (for example the axes ofmovement of the outer drive transfer elements) to be located closertogether. This can result in a more compact arrangement.

The provision of the second, central, drive transfer element on a lowerplane also assists in reducing the bending moment as the drive transferelement is driven, by bringing its axis of movement closer towards theaxis of movement of the corresponding drive assembly interface element.

The retention features of the interface structure 700, for example atleast one of the first fastener and the lug, are shaped and/orconfigured such that when the surgical instrument is detached from thesurgical robot arm, the interface structure is retained on the surgicalrobot arm. The interface structure can be engageable with the instrumentinterface by a second fastener (not shown). The force required todisengage the second fastener is less than the force required todisengage the first fastener and/or the lugs. The interface structure ismore securely attached to the surgical robot arm than to the surgicalinstrument. Thus, the interface structure and the drape to which it isincorporated, remain attached to the surgical robot arm duringinstrument exchange. This is important in order to reduce the time takento change instruments, since the interface structure does not need to bere-attached to the robot arm following detachment of an instrument. Itis also important in order to reduce the likelihood of the drape tearingwhen changing instruments, which would cause the sterile operatingenvironment to become contaminated with the non-sterile environment onthe robot arm side of the drape.

The main body 704 of the interface structure 700 is rigid in theillustrated example. In other examples it need not be rigid. At least aportion of the main body 704 can be of a resilient and/or deformablematerial. At least a portion of the main body can be flexible. A portionof the main body can be a flexible material such as a fabric. A portionof the main body can be unconstrained. The resilience, flexibilityand/or unconstrained nature of the portion of the main body can permitand/or accommodate relative movement between the drive transferelements.

Suitably a portion of the main body between the apertures is resilientand/or deformable, for example flexible. Suitably the main body can beformed in whole or in part of a resilient and/or deformable material.The resilient and/or deformable material can comprise one or more ofsilicone, latex, vinyl, butyl, nitrile, neoprene, and a polymer. Theresilient and/or deformable material suitably comprises a material witha low modulus and low hysteresis. The resilient and/or deformablematerial suitably comprises a material with a good strain to failure.

In another example, illustrated schematically in FIG. 10, the interfacestructure comprises one or more movable portions 1010. The movableportion is flexible and/or elastic. For example, the movable portion isa material such as a fabric. Preferably the material is water-resistantto assist in providing the sterile barrier between the robot arm and theinstrument. The material can be constructed of a plastic sheet, forexample made of polyester, polypropylene, polyethylene orpolytetrafluoroethylene (PTFE). The movable portion 1010 reduces thelikelihood that the material of the interface structure ruckles and/orcontrols the extent to which the material of the interface structureruckles, though it need not do this in all examples. The movable portionis arranged to control the manner in which material of the interfacestructure moves as the drive transfer elements 1001, 1002, 1003 move.This can permit control of, and/or reaction to, the tension within thematerial of the interface structure.

The first portion and/or the second portion is attached to the movableportion. In other examples, the first portion can be attached to onemovable portion. The second portion can be attached to another movableportion. The flexible and/or elastic nature of the movable portion canassist in accommodating movement of the first and/or the second portionsrelative to the main body.

In the illustrated example, two reels 1011, 1012 are provided. Each reelis configured to hold and retain an amount of material. Material can berolled onto one or both reels to take up slack in the material betweenthe reels. Material can be rolled off one or both reels to relievetension in the material between the reels. Material can be rolled ontoor off the reels to accommodate movement of the drive transfer elements.

Referring to FIG. 10a , the material between the reels moves to theleft. This is, for example, because the drive transfer element attachedto that material (not shown) is driven to the left by the driveassembly. As a drive assembly interface element to which that drivetransfer element is engaged moves to the left, so will the material heldby the drive transfer element. The right-hand reel 1011 will rotateclockwise, as indicted by the arrow, to feed material from theright-hand reel 1011. This means that material between the drivetransfer element and the right-hand reel 1011 is not exposed to a hightension that might otherwise cause a rupture in the material, and/ordisrupt operation of the interface structure and/or the instrumentinterface. The left-hand reel 1012 can rotate anti-clockwise, asindicated by the arrow, to roll material onto the left-hand reel 1012.This means that material between the drive transfer element and theleft-hand reel 1012 does not become loose. Similarly, if the drivetransfer element moves to the right, material will be fed from theleft-hand reel 1012. Material can be taken up by the right-hand reel1011. Either or both of the left-hand reel 1012 and the right-hand reel1011 need not take up slack in the material. However, maintaining thematerial taut can assist in covering the aperture and in maintaining thesterile barrier.

Referring now to FIG. 10b , where three drive transfer elements 1001,1002, 1003 are provided adjacent one another, three pairs of reels areprovided. This permits each of the three drive transfer elements to moveindependently of one another without such independent movement causingtension to increase in the material of the interface structure. Forexample, the provision of a pair of reels for each drive transferelement can reduce the extent to which the material between the reels,i.e. the movable portion, is exposed to tension, shear forces and/orrupture. This may be compared to an arrangement in which a single pairof reels is provided for a plurality of drive transfer elements, and thepositioning of the material is based, for example, on an average such asa weighted average of the positions of the plurality of drive transferelements.

In the illustrated example, an uppermost (in the orientation of FIG. 10b) drive transfer element 1001 is moved to the right (as indicated by thearrow), a middle drive transfer element 1002 is moved to the left (asindicated by the arrow) and a lower drive transfer element 1003 is movedto the right (as indicated by the arrow). A first right-hand reel 1013,that of the uppermost section, takes up material of the movable portionand so has a greater reel diameter. A first left-hand reel 1014, that ofthe uppermost section, feeds material of the movable portion from thereel and so has a smaller reel diameter. A second right-hand reel 1015,that of the middle section, feeds material of the movable portion fromthe reel and so has a smaller reel diameter. A second left-hand reel1016, that of the middle section, takes up material of the movableportion and so has a greater reel diameter. A third right-hand reel1017, that of the lower section, takes up material of the movableportion and so has a greater reel diameter. A third left-hand reel 1018,that of the lower section, feeds material of the movable portion fromthe reel and so has a smaller reel diameter.

It will be understood that where the number and/or arrangement of thedrive transfer elements differs from the illustrated example, the numberand/or arrangement of the pairs of reels can similarly differ.

Provision of a reel can assist in reducing the length of the interfacestructure compared to provision of rigid drive transfer elements.Provision of a reel can ensure that the sterile barrier is maintainedwhilst reducing the length of the interface structure needed. This isbecause the reel can take up material that might otherwise haveprojected past (overlapped) the end of the slot when the central portionis adjacent that end of the slot.

Material of the interface structure, such as the movable portion, can betaken up and/or fed from a reel by driving the respective reel about itsaxis. Material of the interface structure can be taken up and/or fedfrom a reel by resiliently biasing the respective reel about its axis.In one example each reel is resiliently biased and is also driven.

Resiliently biasing a reel can assist in keeping tension within thematerial of the interface structure consistent. When tension is lowered(by, for example, a drive transfer element moving towards the relevantreel), the biasing of the reel will cause the reel to rotate so as totake up material. When tension is increased (by, for example, a drivetransfer element moving away from the relevant reel), the biasing of thereel will permit the reel to rotate to as to feed material from thereel.

The resilience of the resilient biasing can be determined to provide fora desired tension or range of tension in the material of the interfacestructure. The resilient biasing is, in one example, provided by aspring coupled to the respective reel.

Driving of the reels can be accomplished by coupling a motor, such as anelectric motor, to each reel. Driving the reels can permit tension to bereleased and/or slack taken up at a desired speed. For example, drivingthe reels can permit tension to be released and/or slack taken up at ahigher speed than might occur with resilient biasing. Driving the reelscan permit tension to be controlled more accurately than by relying onresilient biasing, or on resilient biasing alone.

In one example, one of a pair of reels is coupled to a motor for drivingthat reel, and the other of the pair of reels is resiliently biased. Theresilient biasing adapts to the tension in the material whilst the motoris driven so as to achieve a desired tension. This arrangement permitscontrol of the tension in the material of the interface structure.

A first tension sensor 1021 (shown schematically in FIG. 10a ) iscoupled to the right-hand reel 1011, 1013, 1015, 1017. The first tensionsensor is configured to sense tension in the material between the drivetransfer element and the right-hand reel. The first tension sensor issuitably coupled to a rotational axis of the right-hand reel. A secondtension sensor 1022 (shown schematically in FIG. 10a ) is coupled to theleft-hand reel 1012, 1014, 1016, 1018. The second tension sensor isconfigured to sense tension in the material between the drive transferelement and the left-hand reel. The second tension sensor is suitablycoupled to a rotational axis of the left-hand reel. Tension sensed byeither or both of the first tension sensor and the second tension sensoris used to determine how to drive either or both of the right-hand reeland the left-hand reel. In other words, either or both of the right-handreel and the left-hand reel is controlled in dependence on tensionsensed by either or both of the first tension sensor and the secondtension sensor.

The provision of the first tension sensor and the second tension sensorcan permit a comparison of the tension sensed by each of the first andsecond tension sensors. This comparison can be used to detect rupture orother damage in the material. For example, if the tension sensed at bothof a pair of reels reduces as a drive transfer element moves, it can bedetermined that the material between the reels has ruptured.

In some examples, only one tension sensor need be provided for each of apair of reels.

In an alternative configuration of the interface structure, the aperturein the main body can be a single aperture. In this configuration where asingle drive transfer element is provided, it can engage with the mainbody of the interface structure as described above. Where two or moredrive transfer elements are provided within a single aperture of themain body, the adjacent edges of the drive transfer elements can beprovided with tongue and groove features to enable the drive transferelements to engage with one another. This can assist in restrictingfluid flow paths between the drive transfer elements. It can alsotherefore assist in maintaining the sterile barrier.

Taking as an example a configuration in which three drive transferelements are provided, with the first drive transfer element beingprovided to one side, the third drive transfer element being provided tothe other side, and the second drive transfer element being providedbetween the first and the third drive transfer elements, tongue andgroove type engagements can be provided between the first and the seconddrive transfer elements and between the second and the third drivetransfer elements. The first and third drive transfer elements canengage with the main body of the interface structure as described above.In this configuration, the first drive transfer element can comprise (onits side adjacent the second drive transfer element) one of a firsttongue and a first groove. The second drive transfer element cancomprise (on its side adjacent the first drive transfer element) theother of the first tongue and the first groove. The first tongue isengageable with the first groove. The second drive transfer element cancomprise (on its side adjacent the third drive transfer element) one ofa second tongue and a second groove. The third drive transfer elementcan comprise (on its side adjacent the second drive transfer element)the other of the second tongue and the second groove. The second tongueis engageable with the second groove. This arrangement can permit thefirst drive transfer element to slide along the second drive transferelement and the second drive transfer element to slide along the thirddrive transfer element. This approach thus allows relative movementbetween adjacent drive transfer elements whilst still restricting fluidflow paths between the drive transfer elements.

An example of such an arrangement is shown in FIG. 11. FIG. 11aschematically illustrates an end view of three drive transfer elements.FIG. 11b schematically illustrates a perspective view of the three drivetransfer elements of FIG. 11a . The first drive transfer element 1101comprises an engagement feature such as a lip (not shown) to engage withan edge of the aperture as described above. The first drive transferelement 1101 comprises the first groove 1104 on the side adjacent thesecond drive transfer element 1102. The second drive transfer elementcomprise the first tongue 1105 on the side adjacent the first drivetransfer element 1101. The first tongue is engageable with the firstgroove so as to engage the first drive transfer element with the seconddrive transfer element. The second drive transfer element 1102 comprisesthe second tongue 1106 on the side adjacent the third drive transferelement 1103. The third drive transfer element comprises the secondgroove 1107 on the side adjacent the second drive transfer element. Thesecond tongue is engageable with the second groove so as to engage thesecond drive transfer element with the third drive transfer element. Theother side of the third drive transfer element 1103 comprises anengagement feature such as a lip (not shown) to engage with an edge ofthe aperture as described above. Protrusions 1108 are also schematicallyshown (these have been omitted from FIG. 11b for clarity). Theprotrusions are for engaging with recesses as described above. Recessescould instead be provided. Any combination of protrusions and recessescould be provided.

The outer boundary of the interface structure terminates in a steriledrape (not shown). The sterile drape shrouds the surgical robot arm. Theinner boundary of the interface structure may terminate in a sterilemembrane (not shown) which extends over the hollow interior to isolatethe sterile environment from the non-sterile drive assembly.

The interface structure may be packaged with the drape, for example in aflat configuration.

Suitably, the interface structure 700 is fastened to the drive assemblyas the robot arm is being shrouded in the sterile drape as part of theset-up procedure prior to the operation beginning. An instrument issubsequently fastened to the interface structure 700. At some pointduring the operation, the instrument is exchanged for anotherinstrument. A different instrument can then be attached to the interfacestructure. Providing the interface structure, and retaining theinterface structure on the robot arm when removing an instrument meansthat instruments can be quickly and easily detached from and attached tothe robot arm during an operation without exposing the patient to anon-sterile environment.

The instrument could be used for non-surgical purposes. For example, itcould be used in a cosmetic procedure. The interface structure may beused for non-surgical purposes. The barrier provided by the interfacestructure can be a barrier to fluid flow and/or a barrier to particulatematter, for example particulate matter entrained in a flow of fluid suchas air.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such individual feature or combination offeatures. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention.

1. An interface structure for detachably interfacing a surgical robotarm to a surgical instrument, the interface structure comprising: a mainbody; and a plurality of drive transfer elements, each comprising afirst portion and a second portion, the first portion being releasablyengageable with a respective portion of the surgical robot arm and thesecond portion being releasably engageable with a respective portion ofthe surgical instrument; each of the drive transfer elements beingmovable relative to the main body so as to enable transfer of drivebetween the surgical robot arm and the surgical instrument, wherein themain body defines a plurality of linear paths, at least two of which areof differing lengths, along a respective one of which a respective oneof the drive transfer elements is movable.
 2. An interface structure asclaimed in claim 1, in which the main body comprises a first side forfacing the surgical robot arm and a second side for facing the surgicalinstrument, the first portion being disposed towards the first sideand/or the second portion being disposed towards the second side.
 3. Aninterface structure as claimed in claim 2, in which the main bodycomprises an aperture connecting the first side and the second side, andthe plurality of drive transfer elements is configured so as to obstructfluid flow through the aperture so as to maintain a sterile barrierbetween the surgical robot arm and the surgical instrument.
 4. Aninterface structure as claimed in claim 3, the interface structure beingconfigured so that the plurality of drive transfer elements obstructsfluid flow through the aperture as the drive transfer element movesrelative to the main body.
 5. An interface structure as claimed in claim1, in which the plurality of drive transfer elements covers theaperture.
 6. An interface structure as claimed in claim 1, in which eachof the plurality of paths defined by the main body comprises a channelwithin which a respective one of the plurality of drive transferelements is receivable and along which the drive transfer element ismovable.
 7. An interface structure as claimed in claim 6, comprising acover attachable to the main body, the channel being defined between aportion of the main body and a portion of the cover.
 8. An interfacestructure as claimed in claim 7, in which the cover is attachable to oneof the first side and the second side of the main body.
 9. An interfacestructure as claimed in claim 8, in which each drive transfer elementcomprises a central portion, the central portion comprising the firstportion and the second portion, and an extending portion which extendsaway from the central portion.
 10. An interface structure as claimed inclaim 9, in which the extending portion is configured so that at an endof a range of motion of the drive transfer element relative to the mainbody, a distal end of the extending portion remains covered by thecover.
 11. An interface structure as claimed in claim 1, in which eachdrive transfer element is a rigid element.
 12. An interface structure asclaimed in claim 1, in which the plurality of drive transfer elementscomprises a portion of movable material to which at least one of thefirst portion and second portion are attachable, the movable materialbeing movable so as to accommodate movement of the plurality of drivetransfer elements relative to the main body whilst permitting themaintenance of the sterile barrier between the surgical robot arm andthe surgical instrument.
 13. An interface structure as claimed in claim12, in which the interface structure comprises a roller, and the portionof movable material is windable onto the roller.
 14. An interfacestructure as claimed in claim 1, in which the interface structurecomprises a first drive transfer element movable relative to the mainbody along a first linear path, and a second drive transfer elementmovable relative to the main body along a second linear path, the firstpath and second path being parallel to one another.
 15. An interfacestructure as claimed in claim 14, in which the first path is parallel toa shaft of a surgical instrument when the interface structure isinterfaced with the surgical instrument.
 16. An interface structure asclaimed in claim 1, in which the main body of the interface structurecomprises at least one of a deformable material, a resilient materialand an unconstrained portion.
 17. An interface structure as claimed inclaim 1, in which the main body comprises a first retention portion forretaining the interface structure on at least one of the surgical robotarm and the surgical instrument, the retention portion being engageablewith a second retention portion on the at least one of the surgicalrobot arm and the surgical instrument.
 18. An interface structure asclaimed in claim 1, in which the main body comprises an alignmentfeature on at least one of the first side and the second side for aidingalignment of the interface structure with the surgical robot arm and/orthe surgical instrument during engagement.
 19. An interface structure asclaimed in claim 1, in which a surgical drape extends from the interfacestructure.
 20. A robotic surgical system comprising an interfacestructure as claimed in claim 1 and a surgical robot arm, the surgicalrobot arm comprising a base and a plurality of articulations connectingthe base to a drive assembly interface at or towards a distal end of thesurgical robot arm, the plurality of articulations enabling the driveassembly interface to be articulated relative to the base; the interfacestructure being attachable to the drive assembly interface.